Active housing dual lead assembly

ABSTRACT

A subcutaneous cardiac device includes a subcutaneous electrode and a housing coupled to the subcutaneous electrode by a lead with a lead wire. The subcutaneous electrode is adapted to be implanted in a frontal region of the patient so as to overlap a portion of the patient&#39;s heart.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/150,434, filed on May 17, 2002 and entitled SUBCUTANEOUS CARDIACSTIMULATOR DEVICE HAVING AN ANTERIORLY POSITIONED ELECTRODE, now U.S.Pat. No. 7,149,575; which is a continuation-in-part of application Ser.No. 10/011,956, filed on Nov. 5, 2001, entitled FLEXIBLE SUBCUTANEOUSIMPLANTABLE CARDIOVERTER-DEFIBRILLATOR, now U.S. Pat. No. 7,120,495;which is a continuation-in-part of application Ser. No. 09/940,599,filed on Aug. 27, 2001, entitled CANISTER DESIGN FOR IMPLANTABLECARDIOVERTER-DEFIBRILLATORS, now U.S. Pat. No. 6,950,705; which is acontinuation-in-part of application Ser. No. 09/663,607, filed on Sep.18, 2000, entitled SUBCUTANEOUS ONLY IMPLANTABLE CARDIOVERTERDEFIBRILLATOR AND OPTIONAL PACER, now U.S. Pat. No. 6,721,597 and acontinuation-in-part of application Ser. No. 09/663,606, filed on Sep.18, 2000, entitled UNITARY SUBCUTANEOUS ONLY IMPLANTABLE CARDIOVERTERDEFIBRILLATOR AND OPTIONAL PACER, now U.S. Pat. No. 6,647,292; thedisclosures of which are all incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a device and method for performingelectrical cardiac stimulation, including: cardioversion, defibrillationand, optionally, pacing of the heart using subcutaneous electrodes. Morespecifically, the present invention relates to implantablecardioverter-defibrillator having at least one subcutaneous electrode,wherein the electrode is positioned generally in the frontal portion ofthe thorax, thereby creating a substantially uniform electric fieldacross a patient's heart.

BACKGROUND OF THE INVENTION

The heart is a mechanical pump that is stimulated by electricalimpulses. The mechanical action of the heart results in blood flowthrough a person's body. During a normal heartbeat, the right atrium(RA) of the heart fills with blood from veins within the body. The RAthen contracts and blood is moved into the heart's right ventricle (RV).When the RV contracts, blood held within the RV is then pumped into thelungs. Blood returning from the lungs moves into the heart's left atrium(LA) and, after LA contraction, is pumped into the heart's leftventricle (LV). Finally, with the contraction of the left ventricle,blood from the LV is pumped throughout the body. Four heart valves keepthe blood flowing in the proper directions during this process.

The electrical signal that drives the heart's mechanical contractionstarts in the sino-atrial node (SA node). The SA node is a collection ofspecialized heart cells in the right atrium that automaticallydepolarize (change their potential). The depolarization wavefront thatemanates from the SA node passes across all the cells of both atria andresults in the heart's atrial contractions. When the advancing wavefrontreaches the atrial-ventricular (AV node), it is delayed so that thecontracting atria have time to fill the ventricles. The depolarizingwavefront then passes across the ventricles, causing them to contractand to pump blood to the lungs and body. This electrical activity occursapproximately 72 times a minute in a normal individual and is callednormal sinus rhythm.

Abnormal electrical conditions can occur that can cause the heart tobeat irregularly; these irregular beats are known as cardiacarrhythmias. Cardiac arrhythmias fall into two broad categories: slowheart beats or bradyarrhythmia and fast heart beats or tachyarrhythmia.These cardiac arrhythmias are clinically referred to as bradycardia andtachycardia, respectively.

Bradycardia often results from abnormal performance of the AV node.During a bradycardial event, stimuli generated by the heart's ownnatural pacemaker, the SA node, are improperly conducted to the rest ofthe heart's conduction system. As a result, other stimuli are generated,although their intrinsic rate is below the SA node's intrinsic rate.Clinical symptoms associated with bradycardia include lack of energy anddizziness, among others. These clinical symptoms arise as a result ofthe heart beating more slowly than usual.

Bradycardia has been treated for years with implantable pacemakers.Their primary function is to monitor the heart's intrinsic rhythm and togenerate a stimulus strong enough to initiate a cardiac contraction inthe absence of the heart's own intrinsic beat. Typically, thesepacemakers operate in a demand mode in which the stimulus is appliedonly if the intrinsic rhythm is below a predetermined threshold.

Tachycardia often progresses to cardiac fibrillation, a condition inwhich synchronization of cell depolarizations is lost, and instead,there are chaotic, almost random electrical stimulations of the heart.Tachycardia often results from ischemic heart disease in which localmyocardium performance is compromised and coordinated contraction ofheart tissue is lost which leads to a loss of blood flow to the rest ofthe body. If fibrillation is left untreated, brain death can occurwithin several minutes, followed by complete death several minuteslater.

Application of an electrical stimulus to a critical mass of cardiactissue can be effective to cause the heart to recover from its chaoticcondition and resume normal coordinated propagation of electricalstimulation wavefronts that result in the resumption of normal bloodflow. Thus, the application of an electrical stimulus can revert apatient's heart to a sinus cardiac rhythm and the chambers of the heartonce again act to pump in a coordinated fashion. This process is knownas defibrillation.

Cardioversion/defibrillation is a technique employed to counterarrhythmic heart conditions including some tachycardias in the atriaand/or ventricles. Typically, electrodes are employed to stimulate theheart with high energy electrical impulses or shocks, of a magnitudesubstantially greater than the intrinsic cardiac signals. The purpose ofthese high energy signals is to disrupt the generation of the chaoticcardiac signals and cause the heart to revert to a sinus rhythm.

There are two kinds of conventional cardioversion/defibrillationsystems: internal cardioversion/defibrillation devices, or ICDs, andexternal automatic defibrillators, or AEDs. An ICD generally includes ahousing containing a pulse generator, electrodes and leads connectingthe electrodes to the housing. Traditionally, the electrodes of the ICDare implanted transvenously in the cardiac chambers, or alternatively,are attached to the external walls of the heart. Various structures ofthese types are disclosed in U.S. Pat. Nos. 4,603,705; 4,693,253;4,944,300; 5,105,810; 4,567,900; and 5,618,287, all incorporated hereinby reference.

In addition, U.S. Pat. Nos. 5,342,407 and 5,603,732, incorporated hereinby reference, disclose an ICD with a pulse generator implanted in theabdomen and two electrodes. In one embodiment (FIG. 22), the twoelectrodes 188, 190 are implanted subcutaneously and disposed in thethoracic region, outside of the ribs and on opposite sides of the heart.In another embodiment (FIG. 23), one electrode 206 is attached to theepicardial tissues and another electrode 200 is disposed inside the ribcage. In a third embodiment (FIG. 24), one electrode 208 is disposedaway from the heart and the other electrode 210 is disposed inside theright ventricle. This system is very complicated and it is difficult toimplant surgically.

Recently, some ICDs have been made with an electrode on the housing ofthe pulse generator, as illustrated in U.S. Pat. Nos. 5,133,353;5,261,400; 5,620,477; and 5,658,325, all incorporated herein byreference.

ICDs have proven to be very effective for treating various cardiacarrhythmias and are now an established therapy for the management oflife threatening cardiac rhythms, such as ventricular fibrillation.However, commercially available ICDs have several disadvantages. First,commercially available ICDs must be implanted using somewhat complex andexpensive surgical procedures that are performed by specially trainedphysicians. Moreover, lead placement procedures require special roomequipped for fluoroscopy. These rooms are limited in number andtherefore, limit the number of lead placement procedures, and ultimatelythe number of ICDs, that may be implanted in any given day.

Second, commercially available ICDs rely on transvenous leads for theplacement of at least one electrode within the cardiac chambers. It hasbeen found that over a period of time, transvenous lead electrodes mayget dislodged from the cardiac tissues. Additionally, complications suchas broken leads and undesirable tissue formations deposits on theelectrodes are not uncommon. These problems are especially acute whenleads carry two or more electrodes. Moreover, infection is a concernwhen implanting leads within a patient's vasculature.

Third, removing these ICDs and replacing them, if necessary, alsorequires complicated surgical procedures that may be morelife-threatening than the initial implantation.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a subcutaneous cardiacstimulator device adapted to generate an electric field across the heartusing at least one subcutaneous electrode positioned at a locationselected to minimize the degree of surgical intervention.

In yet another embodiment, the present invention provides a subcutaneouscardiac stimulator device that does not include any leads extendinginto, or touching, a patient's heart or venous system. The electrodescan be positioned in a sternum position, a lateral position, an upperand/or a lower position with respect to the heart.

The present invention provides a device which, in one embodiment, has acurvilinear electrode that is positioned subcutaneously in the frontalor chest area of the body such that it overlaps a peripheral region ofthe heart. The term ‘curvilinear electrode’ is used herein to designatean electrode having an elongated configuration with a substantiallyuniform cross-section along its length and having a cross-sectionaldiameter that is much smaller than its length by at least an order ofmagnitude.

The housing of the ICD device of the present invention can be active orinactive. If the housing is active, it is implanted in a positionselected to generate an electric field with the electrode so thatcurrent passes through the heart and is effective to induce shockstherein. If the housing is inactive, then a separate electrode is alsoimplanted subcutaneously and cooperates with the first electrode togenerate the required electric field. Moreover, housing embodiments ofthe present invention can be implanted in a side position, aninframammary position or a pectoral position in the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a subcutaneous cardiac device having oneor two subcutaneous electrodes constructed in accordance with thisinvention;

FIG. 2A is a diagrammatic view of the chest or frontal region of thepatient with some of the possible electrode and housing positions inaccordance with this invention;

FIG. 2B is a partial diagrammatic view of the side of the patientshowing possible positions of the electrode and the housing;

FIGS. 3A and 3B show a frontal view and a side view of an active housingin the inframammary position and an electrode in the upper position;

FIGS. 3C and 3D show the electrical field generated with theconfiguration of FIGS. 3A and 3B, respectively;

FIGS. 4A and 4B show a frontal and a side view of an inactive housing inthe inframammary position with an electrode in the sternum and a secondelectrode in the lateral position;

FIGS. 4C and 4D show frontal view and a top view of the electrical fieldgenerated in the configuration of FIGS. 4A and 4B;

FIGS. 5A and 5B show a frontal view and a side view of an active housingin the side position and an electrode in the sternum position;

FIGS. 6A and 6B show a frontal view and a side view of an inactivehousing in the side position and electrodes in the top and lowerpositions;

FIGS. 7A and 7B show a frontal view and a side view of an active housingin the pectoral position and an electrode in the lower position;

FIGS. 8A and 8B show a frontal view and a side view of an inactivehousing in the pectoral position and electrodes in the sternum andlateral positions;

FIGS. 9A and 9B show a frontal view and a side view of an inactivehousing on the right side of the heart and electrodes in the top andlower positions;

FIGS. 10A and 10B show a frontal view and a side view of an activehousing in the inframammary position and an electrode in sternumposition;

FIGS. 10C and 10D show a frontal and a top view of the electrical fieldgenerated by the configuration of FIGS. 10A and 10B;

FIGS. 11A and 11B show a frontal and a side view of an active housing inthe side position and an electrode in the lower position;

FIGS. 12A and 12B show a frontal and a side view of an active housingand two electrodes in the sternum and lateral positions;

FIG. 12C shows the electrical field generated by one embodiment of theFIG. 12A configuration;

FIG. 13A shows a frontal view of an active housing in the side positionwith electrodes in the upper and lower positions;

FIG. 13B shows a frontal view of an active housing in the inframammaryposition and electrodes in the sternum and lateral positions;

FIGS. 14A-14D show frontal view configuration of an active housing withan electrode positioned on either side of the sternum;

FIGS. 15A-15D show an active housing, a segmented electrode and variousstimulations applied therebetween;

FIG. 16 shows an active housing and two electrodes disposed adjacent tothe sternum; and

FIG. 17 shows an active housing and two electrodes disposed adjacent tothe sternum, one of the electrodes being multi-segmented.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, FIG. 1 shows an implantable cardiacdevice 10 constructed in accordance with one embodiment of the presentinvention. The device 10 includes a housing 12 containing a pulsegenerator (not shown), an electrode 14 and a lead 16. The electrode 14is connected to the pulse generator through a header 18 disposed on thehousing 12.

In particular embodiments of the present invention, the housing 12 canact as an active housing. In this embodiment, the housing 12 itself,comprises a second electrode for the ICD device 10. An active canisterhousing 12 is formed either with a continuously conductive surface, orwith a separate conductive zone 20. The conductive surface or zone 20 ofan active canister housing 12 is connected electrically to the circuitrydisposed in the housing 12. If the whole housing 12 is used as an activeelectrode, then its surface area presents a low interface resistancewith the patient's tissues, thereby lowering the losses in thetissue/electrode interface. In alternative embodiments, the housing 12maybe inactive, in which case the housing 12 is electrically isolatedfrom its internal circuitry.

FIG. 1 further depicts a second electrode 14′ that is connected to theheader 18 by a second lead 16′. Particular embodiments of the presentinvention may utilize a second 16′ or third (not shown) lead withoptional electrode.

The housing 12 can be a conventional defibrillator housing used forprogrammable electronic circuitry that senses intrinsic cardiac activityand generates antiarrhythmic therapy (defibrillation shocks and/orpacing pulses) in the usual manner. To facilitate implantation, thecircuitry contained within the housing can also induce ventricularfibrillation for the purposes of testing the defibrillation threshold(DFT). DFT testing can be accomplished by delivering a shock during thevulnerable period of the cardiac cycle (T-wave) or by rapid pacingapproximately 20 to 100 Hz for several seconds or by the application ofdirect current for several seconds or by the alternating current between20 and 100 Hz for several seconds.

In particular embodiments, the housing 12 has a generally oval shape ora square shape with rounded corners. Although the housing 12 isillustrated as being square or rectangular, the housing 12 may alsocomprise any additional shapes conventionally known in the art.Moreover, the housing 12 is made of titanium and/or other similarbiocompatible materials commonly used for implantable devices.

The housing 12 generally comprises a footprint in the range of 30-50 cmand maybe about 1.2 cm deep.

Electrode 14 is a subcutaneous electrode that is positioned under theskin and refrains from directly contacting the patient's heart. Thesubcutaneous electrode 14 may embody numerous shapes and sizes. Forexample, the electrode 14 may be planar, or may have a cross section ofother shapes, e.g. circular. The electrode could be made from a coil, itcould be braided or woven, or could be made by other similar means. Inparticular embodiments of the present invention, the electrode 14 is acurvilinear electrode. The term ‘curvilinear electrode’ is used hereinto designate an electrode having an elongated rod-shaped configurationwhich could be straight or could be somewhat curved, and have asubstantially uniform cross-section along its length and having across-sectional diameter that is much smaller than its length by atleast an order of magnitude. Generally, the electrode 14 has a length ofabout 2-10 cm and a diameter of about 1-5 mm.

In electrodes 14 that are curvilinear, the tip of the electrode 14 maybe rounded or formed with a dull point, as at 19 to assist itsimplantation. The electrode 14, or at least its outer surface, is madeof an electrically conducting biocompatible material. The electrode 14is preferably made of the titanium or stainless steel. Other electrodematerials, conventionally known in the art, may additionally be used toform the electrode 14. In addition, particular electrode 14 embodimentsmay be coated with platinum or platinum alloy such as platinum iridium.

In general, the electrode 14 is flexible. Implanting a flexibleelectrode 14 minimizes discomfort associated with the implantation ofthe electrode 14 within the patient. In order to facilitate insertion ofthe electrode 14 within the patient, additional supporting mechanismsmay be utilized during the insertion process. For example, a removablestylet may be used during the insertion process. After the electrode isproperly positioned within the patient, the stylet is then removed fromthe electrode 14 (for example, from within the aperture formed from acoil electrode); rendering the electrode 14 flexible to conform to thepatient's body for its duration. Additional insertion mechanisms, knownin the art, may also be utilized to insert the flexible electrode 14.One insertion mechanism, for example, is the use of a peal away rigidsheath.

The electrode(s) and the housing 12 can be implanted using variousconfigurations. While these configurations differ in the positioning ofthe electrode(s) and the housing 12, what they have in common is thatleast one electrode is disposed in the frontal or anterior region of thepatient. The housing or the other electrode is then positioned so thatit interfaces with the first electrode to generate an electrical fieldthat passes through the heart and is effective to defibrillate theheart. In particular embodiments, the at least one electrode is disposedin the frontal or anterior region such that it overlaps a peripheralregion of the heart as viewed from the front.

Four electrode positions and three housing positions are identified inFIGS. 2A and 2B. In these Figures, the heart is designated by the letterH, the sternum is indicated by an axis ST, the collar bone is indicatedby a line CB and the inframammary crease is indicated by line IC. Thelateral outline of the rib cage is indicated by line R and the skinextending outwardly from the rib cage laterally under the armpit isdesignated by the line SU, while the skin disposed in front of the ribcage is indicated by line SF. Obviously FIGS. 2A and 2B are not toscale, and the various tissues and bone structures shown therein areused to identify the relative locations of the electrode(s) 14, 14′ andthe housing 12 with respect to these physiological landmarks. Thetunneling path used for the electrode placement is not necessaryrepresented by the path indicated by the lead 16.

Four electrode positions are defined herein as positions A, B, C and D.As seen in the Figures, position A is a vertical position on the rightside of the heart adjacent to the sternum. This position A is designatedherein as the sternum position. Position B is disposed on the left sideof the heart opposite from position A. Position B is also designatedherein as the lateral position. Position C is a substantially horizontalposition near the top of the heart and is designated herein as the upperposition. Finally, position D is a substantially horizontal positionnear the bottom of the heart and is designated the lower position.

It is important to note that all four of these electrode positions aredisposed subcutaneously, i.e., between the rib cage R and the skin SF inthe frontal or anterior chest area. Several of these electrodespositions are further depicted overlapping either the top, bottom, leftor right peripheral region of the heart.

The tissues bounded by these four electrode positions are generallyfatty tissues and/or comprise bony material—both having a relativelyhigh electrical resistivity as compared to the resistivity of thecardiac tissues. Positioning the electrodes in the frontal or anteriorchest area allow the naturally forming resistivity differential tobetter force electric current through the patient's heart, rather thanshunting into surrounding tissue.

Because the electrode placement of the present invention refrains fromaccessing the vasculature of the patient, serious risks of infection aregreatly reduced. Infections arising from the present invention would bemore likely localized and easily treatable. Whereas, infections arisingfrom prior art devices that utilize leads that access the patient'svasculature, tend to pose more serious risks to the patient's health.

In addition, positioning the electrodes in the frontal or anterior chestarea eliminates the requirement of fluoroscopy. The use of fluoroscopyadds additional cost and risks to an ICD implantation procedure.Specifically, the physician must wear protective lead shielding andutilize specially designed electrophysiology laboratories equipped forfluoroscopy. Electrode placement in the present invention, however,follows predominant anatomical landmarks that are easily accessible, andare highly identifiable. Fluoroscopy, therefore, is not required becausethe ICD embodiments of the present invention are positioned in thesubcutaneous frontal portion of the patient's chest, which is readilyaccessible to a physician without the need for fluoroscopy.

FIGS. 2A and 2B show three subcutaneous positions X, Y, Z for thehousing 12. Position X is disposed on the left side of the rib cage,under the arm, and is designated herein as the side position. Position Yis a frontal position, under the inframammary crease IC and isdesignated herein as the inframammary position. Finally, position Z isalso a frontal position and it corresponds to the conventional positionfor ICDs, above and to the left of heart under the collarbone CB. Thisposition Z is designated herein as the pectoral position.

In the following discussion, the various configurations are nowdescribed with the housing being disposed at one of the locations X, Yor Z. Except as noted, for each housing position, two electrodeconfigurations are disclosed: one for an active housing and a singleelectrode; and a second for an inactive housing, a first electrode and asecond electrode.

In FIGS. 3A and 3B, the housing 12 is an active housing and is shownimplanted at position Y, or inframammary position. The electrode 14 isdisposed horizontally in the upper position C. The lead 16 is threadedsubcutaneously to the device. As illustrated in the Figures, the housing12 and electrode 14 are both disposed outside the front portion of therib cage, with the housing 12 being disposed below the heart H and theelectrode 14 being disposed in the upper position at a level with thetop portion of the heart H. Thus, in this embodiment, the housing 12 andthe electrode 14 are positioned above and below the center of the heartC.

The tissues between the housing 12 and the electrode 14 are fattytissues and/or bony material that have a much higher resistivity thenthat of the muscle between the ribs. Therefore, when a voltage isapplied between the electrode 14 and the housing, current naturallyfollows the path of least resistance. In the position illustrated inFIGS. 3A and 3B, as with all the other embodiments depicted in theFigures herein, the applied voltage follows the lower conductivity ofthe heart muscle, and not the fat or bone. The electric field formedacross the heart by this position is shown in detail in FIGS. 3C and 3D.Thus, the positions illustrated better direct a sufficient amount ofcurrent to be forced through the heart causing its defibrillation.

In FIGS. 4A and 4B, the housing 12 is an inactive housing shownimplanted in the inframammary position Y and electrodes 14 and 14′ areimplanted in the sternum and lateral positions A and B, respectively. Inthis case, the electric field is established between the electrodes 14and 14′, as illustrated in FIGS. 4C and 4D. Again, because the tissuesbetween the electrodes are fatty tissues and/or bony material, they havea higher resistivity then the cardiac tissues, and accordingly, electriccurrent flows through the heart, rather than along a direct path betweenthe two electrodes.

In FIGS. 5A and 5B, the housing 12 is an active housing implanted in theside position X and electrode 14 is in the sternum position A.

In FIGS. 6A and 6B, the housing 12 is an inactive housing implanted atthe side position X and the electrodes 14, 14′ are oriented horizontallyat the upper and lower positions C and D, respectively.

In FIGS. 7A and 7B, the housing 12 is an active housing disposed at thepectoral position Z and electrode 14 is oriented horizontally at thelower position D.

In FIGS. 8A and 8B, the housing 12 is an inactive housing disposed atthe pectoral position Z and electrodes 14 and 14′ are arrangedvertically at the sternum position A and lateral position B,respectively.

In FIGS. 9A and 9B, the housing 12 is inactive and is positioned abovethe heart, between the electrodes 14, 14′ in positions C and D,respectively.

In the configurations described so far, an electric field is generatedbetween a first electrode disposed horizontally or vertically along afront portion of the rib cage and either the housing or a secondelectrode disposed on an opposite side of the heart. However, otherconfigurations may also be used in which the second electrode or housingis disposed along the front portion of the rib cage at a right anglewith respect to a longitudinal axis of the first electrode. One suchconfiguration is shown in FIGS. 10A and 10B. In this configuration, thefirst electrode 14A is disposed in the sternum position A and thehousing 12 is disposed in the inframammary position Y. As seen in FIGS.10C and 10D (FIG. 10D being a top view), when a voltage is applied tobetween these two elements, an electric field is generated through theheart. However, the linear distance between the two elements generatingthe field has to be sufficiently large to insure that a substantialportion of the electric current passes through the heart and is notshunted directly between the first electrode and the housing. For thisreason, the electrode in FIGS. 10A and 10B is shorter than theelectrodes in the previous embodiments. For example, the electrode 14Amay have half the length of the other electrodes 14, 14′. In addition,the electrode 14A is positioned as far as possible from the housing 12while still being superimposed on a peripheral region of the heart.

FIGS. 11A and 11B show a configuration in which the active housing is inthe side position X and the electrode 14A is in the lower position andhas a shorter length.

In the following configurations, an active housing 12 is used with twoshort electrodes 14A, 14A′, the two electrodes being shorted to eachother so that the electric field is generated between each electrode andthe housing.

In FIGS. 12A and 12B the active housing 12 is in pectoral position andthe electrodes 14A, 14A′ are in the sternum and lateral positions,respectively. In this configuration, the active housing 12 may generatean electric field with electrode 14A alone. Alternatively, the activehousing 12 may generate an electric field with electrode 14A′ alone.Finally, the active housing 12 may generate an electric field with bothelectrode 14A and electrode 14A′. The electric field created by such anarrangement is depicted in FIG. 12C. In this configuration, the electricfield forms a broad wave front that traverses through the heart.

In FIG. 13A the active housing is in the side position and theelectrodes 14A and 14A′ are in the upper and lower positions,respectively. Similar to FIG. 12A, the active housing 12 may generate atleast three distinct electric fields—with electrode 14A alone, withelectrode 14A′ alone, and with both electrode 14A and electrode 14A′.

In FIG. 13B (which is a front view) the active housing is in theinframammary position and the electrodes 14A, 14A′ are in the sternumand lateral positions, respectively.

In the following configurations, an electric field is generated betweena first electrode disposed horizontally along a front portion of the ribcage and a housing disposed on the opposite side of the sternum. Theseembodiments describe a fifth and sixth electrode placement (C′ and D′,respectively). Moreover these embodiments encompass a fourth and fifthhousing placement (Y′ and Z′, respectively).

In FIG. 14A, the active housing 12 is in the pectoral position on theleft side of the sternum (position Z), and the electrode 14 is in asubstantially lower horizontal position on the right side of the sternum(position D′).

In FIG. 14B, the active housing 12 is in the pectoral position on theright side of the sternum (position Z′), and the electrode 14 is in thesubstantially lower horizontal position on the left side of the sternum(position D).

In FIG. 14C, the active housing 12 is in the inframammary position onthe left side of the sternum (position Y), and the electrode 14 is in asubstantially upper horizontal position on the right side of the sternum(position C′).

In FIG. 14D, the active housing 12 is in the inframammary position onthe right side of the sternum (position Y′), and the electrode 14 is ina substantially upper horizontal position on the left side of thesternum (position C).

The cardiac device 10 can be used to apply defibrillation and pacingtherapy. In the configuration shown in the Figures discussed so far,sensing can be effected by using the same elements that are used fordefibrillation and/or pacing. Induction for DFT testing purposes canalso use the same elements that are used for defibrillation and/orpacing.

Alternatively, separate electrodes can be provided for sensing and/orpacing. In one embodiment shown in FIG. 15A, a segmented electrode 30 isprovided which can have approximately the same length as the electrode14 in FIG. 1. The electrode 30 consists of three segments: an endelectrode 32, an intermediate segment 34 made of a non-conductivematerial and a main electrode 36. The end electrode 32 can have a tipwith a reduced diameter, similar to the tip 19 on electrode 14 in FIG.1.

Preferably the three segments have substantially the same cross sectionso that the electrode 30 can be implanted easily in a tunnel in any ofthe electrode positions discussed above in a manner similar to electrode14. The axial length of end electrode 32 can be up to 50% of the totallength of the segmented electrode 30. The intermediate segment 34 canhave a negligible axial dimension as long as it electrically isolatesthe end electrode 32 from the main electrode 36.

The main electrode 36 is connected to the housing 12 through a lead 38and a connector 40 attached to the header. Similarly, segment 32 isconnected by a lead 42 to header 18 through a connector 44.Alternatively, the two wires 38, 42 can be incorporated into a commonlead 46. In this latter configuration, preferably, the segments 34, 36are hollow to allow the wire 42 to pass therethrough and connect to theend electrode 32, as illustrated in FIG. 15A by the phantom line. Device10A, shown in FIG. 15A, and incorporating electrode 30, housing 12 andlead 46 can be configured to operate in several modes. In one mode,shown in FIG. 15A, sensing and ventricular shocks can be applied betweenthe main electrode 36 and the housing 12, while pacing can be appliedbetween the end electrode 32 and the housing 12. This embodiment isparticularly advantageous because it avoids stimulating the abdomen.

FIGS. 15B, 15C and 15D show other modes of operation. In FIG. 15B a modeis shown wherein pacing, sensing and induction are implemented betweenthe end electrode and the housing and shock is applied between the mainelectrode and the housing. In FIG. 15C pacing and a shock can be appliedbetween the end electrode 32 and the housing 12. Sensing is accomplishedbetween the main electrode 36 and the housing 12. In addition, a shockcan also be applied between the main electrode and the housing 12.Alternatively, during defibrillation the end and the main electrodescould be shorted and shock could be applied between both electrodes andthe housing.

In FIG. 15D, pacing, sensing, induction and a shock is applied betweenthe end electrode and the housing. A shock is additionally appliedbetween the main electrode and the housing.

In the embodiments described so far, a single electrode element isenvisioned that may be segmented but is disposed in a single tunnel atthe various electrode positions. However, it may be advantageous in someinstances to provide two electrode elements. FIG. 16 shows onemulti-element electrode configuration. In this configuration, twoelectrode elements 50 and 52 are provided, each having a structuresimilar to electrode 14 or 14′. The electrode elements are adapted to beimplanted parallel to each other. For example, the two elements can beimplanted on either side of the sternum ST. In this configuration, eachelectrode element 50, 52 is provided with its own lead wire 54, 56coupling the same to the housing 12 through a header 18 and a respectiveconnector (not shown). The lead wires can be provided in a single lead,or in separate leads. Each of these electrode elements 50, 52 can beused for sensing, pacing, induction or shocks

In another multi-electrode element embodiment shown, in FIG. 17, twoelectrode elements 60, 62 are provided. Electrode element 60 is similarto electrode 14 or 14′ in FIG. 1 while electrode element 62 ismulti-segmented, and thus it is similar to the electrode 30 of FIG. 16A.That is, electrode element 62 includes an end electrode 64, anintermediate segment 66 and a main electrode 68. Preferably, in thisembodiment, electrode element 62 and the main electrode 68 areelectrically connected to each other and connected to the housing 12 bya common lead wire 70, while end electrode 64 is connected to thehousing by a second lead wire 72. Alternatively, the electrode element62 could be connected to the end electrode 64. In addition, bothelements 60, 62 could be segmented.

Numerous characteristics and advantages of the invention covered by thisdocument have been set forth in the foregoing description. It will beunderstood, however, that this disclosure is, in many aspects, onlyillustrative. Changes may be made in details, particularly in matters ofshape, size and arrangement of parts without exceeding the scope of theinvention. The invention's scope is defined in the language in which theappended claims are expressed.

1. A method of terminating a cardiac arrhythmia in a patient comprisingdelivering an electrical stimulus between a first implanted electrodedisposed on a canister implanted in the patient and at least one ofsecond and third implanted electrodes also implanted in the patientwherein: the canister houses circuitry for generating and controllingdelivery of the electrical stimulus; each of the first, second and thirdimplanted electrodes is disposed at a subcutaneous location over thepatient's ribcage; the second implanted electrode is disposed in asubstantially vertical position over the patient's heart parallel toand, adjacent the sternum; the third implanted electrode is disposed ina substantially vertical position, parallel to the sternum and left ofthe second implanted electrode; and the canister is disposed superior tothe second and third implanted electrodes.
 2. The method of claim 1,wherein the canister is generally between the second and thirdelectrodes at a position superior thereto.
 3. The method of claim 1,wherein the second implanted electrode and the third implanted electrodeare disposed on first and second lead assemblies each separately coupledto the housing.
 4. The method of claim 1, wherein the electricalstimulus is delivered between the first and second implanted electrodes.5. The method of claim 1, wherein the electrical stimulus is deliveredbetween the first and third implanted electrodes.
 6. The method of claim1, wherein the electrical stimulus is delivered between the firstimplanted electrode and a combination of the second and third implantedelectrodes operating cooperatively.
 7. The method of claim 1, furthercomprising sensing cardiac activity of the patient.
 8. A method ofterminating a cardiac arrhythmia in a patient comprising delivering anelectrical stimulus between a first implanted electrode disposed on acanister implanted in a patient and at least one of second and thirdimplanted electrodes also implanted in the patient, wherein: thecanister houses circuitry for generating and controlling delivery of theelectrical stimulus; each of the first, second and third implantedelectrodes is disposed at a subcutaneous location over the patient'sribcage; the canister is disposed on the left side of the patient'sribcage under the arm; the second implanted electrode is disposed in asubstantially horizontal position near the top of the heart,perpendicular to the sternum, and over the left side of the patient'sribcage; and the third implanted electrode is disposed in asubstantially horizontal position near the bottom of the heart,perpendicular to the sternum, inferior to the second implanted electrodeand over the left side of the patient's ribcage.
 9. The method of claim8, wherein the canister is disposed between the second and thirdimplanted electrodes.
 10. The method of claim 8, wherein the secondimplanted electrode and the third implanted electrode are disposed onfirst and second lead assemblies each separately coupled to the housing.11. The method of claim 8, wherein the electrical stimulus is deliveredbetween the first and second implanted electrodes.
 12. The method ofclaim 8, wherein the electrical stimulus is delivered between the firstand third implanted electrodes.
 13. The method of claim 8, wherein theelectrical stimulus is delivered between the first implanted electrodeand a combination of the second and third implanted electrodes operatingcooperatively.
 14. A method of terminating a cardiac arrhythmia in apatient comprising delivering an electrical stimulus between a firstimplanted electrode disposed on a canister implanted in a patient and atleast one of second and third implanted electrodes also implanted in thepatient wherein: the canister houses circuitry for generating andcontrolling delivery of the electrical stimulus; each of the first,second and third implanted electrodes is disposed at a subcutaneouslocation over the patient's ribcage; the canister is disposed at aboutthe patient's left inframammary crease; the second implanted electrodeis disposed in a substantially vertical position, parallel and adjacentthe sternum; and the third implanted electrode is disposed in asubstantially vertical position, parallel to the sternum and to the leftof the second implanted electrode.
 15. The method of claim 14, whereinthe canister is disposed between the second and third implantedelectrodes.
 16. The method of claim 14, wherein the second implantedelectrode and the third implanted electrode are disposed on first andsecond lead assemblies each separately coupled to the housing.
 17. Themethod of claim 14, wherein the electrical stimulus is delivered betweenthe first and second implanted electrodes.
 18. The method of claim 14,wherein the electrical stimulus is delivered between the first and thirdimplanted electrodes.
 19. The method of claim 14, wherein the electricalstimulus is delivered between the first implanted electrode and acombination of the second and third implanted electrodes operatingcooperatively.
 20. A method of treating a patient comprising: providingan implantable cardioverter defibrillator system comprising: a canisterhousing circuitry for generating and controlling delivery of cardiacstimulus, the canister including a canister implanted electrode disposedthereon; a first lead assembly coupled to the canister and having afirst implanted electrode; and a second lead assembly coupled to thecanister and having a second implanted electrode; wherein the circuitryin the canister is configured to selectively deliver cardiac stimulususing a selected one of the following configurations: canister implantedelectrode and first implanted electrode only; canister implantedelectrode and second implanted electrode only; and canister implantedelectrode and, cooperatively coupled together, second and thirdimplanted electrodes; and implanting the system into a patient such thateach of the canister and implanted electrodes are disposedsubcutaneously over the patient's ribcage; wherein: the implanting stepis performed such that the canister is disposed near to and inferior ofthe clavicle, the first implanted electrode is disposed in asubstantially vertical position, parallel and adjacent to the sternum,and the second implanted electrode is disposed in a substantiallyvertical position, parallel to the sternum and to the left of the secondimplanted electrode, with the canister being superior to each of thefirst and second implanted electrodes.
 21. A method of treating apatient comprising: providing an implantable cardioverter defibrillatorsystem comprising: a canister housing circuitry for generating andcontrolling delivery of cardiac stimulus, the canister including acanister implanted electrode disposed thereon; a first lead assemblycoupled to the canister and having a first implanted electrode; and asecond lead assembly coupled to the canister and having a secondimplanted electrode; wherein the circuitry in the canister is configuredto selectively deliver cardiac stimulus using a selected one of thefollowing configurations: canister implanted electrode and firstimplanted electrode only; canister implanted electrode and secondimplanted electrode only; and canister implanted electrode and,cooperatively coupled together, second and third implanted electrodes;and implanting the system into a patient such that each of the canisterand implanted electrodes are disposed subcutaneously over the patient'sribcage; wherein: the implanting step is performed such that thecanister is disposed over the left side of the patient's ribcage andunder the patient's arm, the first implanted electrode is disposed in asubstantially horizontal position near the top of the heart andperpendicular to the sternum, and the second implanted electrode isdisposed in a substantially horizontal position near the bottom of theheart, perpendicular to the sternum, and inferior to the first implantedelectrode.
 22. A method of treating a patient comprising: providing animplantable cardioverter defibrillator system comprising: a canisterhousing circuitry for generating and controlling delivery of cardiacstimulus, the canister including a canister implanted electrode disposedthereon; a first lead assembly coupled to the canister and having asecond implanted electrode; and a second lead assembly coupled to thecanister and having a second implanted electrode; wherein the circuitryin the canister is configured to selectively deliver cardiac stimulususing a selected one of the following configurations: canister implantedelectrode and first implanted electrode only; canister implantedelectrode and second implanted electrode only; and canister implantedelectrode and, cooperatively coupled together, second and thirdimplanted electrodes; and implanting the system into a patient such thateach of the canister and implanted electrodes are disposedsubcutaneously over the patient's ribcage; wherein: the implanting stepis performed such that the canister is disposed generally at thepatient's inframammary crease, the first implanted electrode is disposedin a substantially vertical position, parallel and adjacent to thesternum, and the second implanted electrode is disposed in asubstantially vertical position, parallel to the sternum and to the leftof the first implanted electrode.